Study Guide: Tower

Introduction

This Study Guide has been designed to give you all the information needed to start controlling as a Tower controller on the VATSIM network.

Radio Communication - Basics

Because Communication is crucially important for Air Traffic Control a fixed format and syntax us used, in order to minimize the risk of misunderstandings and to keep messages short. Worldwide English is the primary language in use, however in most countries you are also allowed to use the local language. In Austria VFR flights can choose their language whereas IFR flights are mostly conducted in English. Link: Buchstabiertabelle

Basic Rules

In order to achieve the goals set above the following rules important:

Listen before you talk

It's impossible for two radio stations to transmit on the same frequency at the same time. If this is done, the radio signal will be blocked and this will result in a nasty noise on the frequency. Therefore it's important that every station monitors the frequency for about 5 seconds before transmitting, to make sure there’s no ongoing radio traffic. If you hear an ongoing conversation, wait until the conversation is over before you begin to transmit. Don’t start your communication if there is a read-back expected on the last transmission even if there is a short pause.

Think before you talk

The radio traffic flow should be as smooth as possible. To achieve this it's vital to "think first" before transmitting so that a clear, concise and uninterrupted message can be sent.

As far as possible use standard phraseology and syntax

To prevent misunderstandings and to maintain the radio traffic as effective as possible, stick to standardized phraseology and skip slang and of course private messages.

Callsigns and Initial Contact

Every participant on the network has his own Callsign. Controller Positions are identified by their location and their Function (e.g. Wien Radar, Graz Tower), Aircraft either by their Registration (e.g. OE-ALB) or an Airline Callsign followed by a combination of numbers and letters (e.g. AUA25LM, SWR387).
To pronounce these letters and digits the ICAO-Alphabet is used.
To initiate the contact between two stations an initial call has to be made. This call has the following structure:

Station 1: Station 2, Station 1, Message
Station 2: Station 1, Station 2, Message

In Subsequent calls the calling station part can be ommited.
When a controller (or aircraft) transmits a message to a station it is very important that the receiving station acknowledge the message and reads back any required parts.. If the receiving station does not acknowledge, the transmitted message is considered as a lost transmission and the sender should resend the message or check if the receiving station got the message.
Items that must always be read back in full are all clearances (including altitudes, heaings, speeds, radials etc), runway in use, altimeter setting (QNH or QFE) and transition level, and all frequencies. For a controller, this is extremely important to remember, since if a pilot's readback is incorrect, the controller has to ask for confirmation, i.e a new readback. There are also items that should not be read back to reduce unnesessary radio transmissions. In short, this includes everything not mentioned above, but a few examples are: wind, temperature and other weather information (except altimeter settings) and traffic information in detail.
When giving an instruction the Callsign is stated at the beginning, when reading back you usually add it at the end of your transmission (although you are allowed to do it at the beginning too).

Working Delivery Positions

Clearence Delivery is responsible for checking and correcting flightplans of departing aircraft and issue routing clearances to them.

Flightplan Structure

Flight plans are documents filed by pilots with the local Civil Aviation Authority prior to departure. They generally include basic information such as departure and arrival points, estimated time en route, alternate airports in case of bad weather, type of flight (whether instrument flight rules or visual flight rules), pilot's name and number of people on board.
For IFR flights, flight plans are used by air traffic control to initiate tracking and routing services. For VFR flights, their only purpose is to provide needed information should search and rescue operations be required.

Routing Types
Aircraft routing types used in flight planning are: Airway, Navaid and Direct. A route may be composed of segments of different routing types.

Airway
Airway routing occurs along pre-defined pathways called Airways. Mostly aircraft are required to fly airways between the departure and destination airports. The rules cover altitude, airspeed, and requirements for entering and leaving the airway (SIDs and STARs).
Navaid
Navaid routing occurs between Navaids (short for Navigational Aids) which are not always connected by airways. Navaid routing is typically only allowed in the continental U.S. If a flight plan specifies Navaid routing between two Navaids which are connected via an airway, the rules for that particular airway must be followed as if the aircraft was flying Airway routing between those two Navaids. Allowable altitudes are covered in Flight Levels.

Direct
Direct routing occurs when one or both of the route segment endpoints are at a latitude/longitude which is not located at a Navaid.

Issuing IFR Routing Clearances

DEL gives routing clearances to all departing aircraft with the following information:

Destination of aircraftSID (= Standard instrument departure) Normally the filed SID is given
Initial climb altitude after departure (5000ft)
Squawk (Squawk assignments for LOWW are 4600 to 4620)
QNH (Local QNH of airport according to latest METAR)
CTOT (= Calculated take-off time) Slot time (Normally not used on the VATSIM network)

Taxi Instructions

In this way, collision of aircraft should be avoided. Incoming aircraft on runway 16/34 vacating via B3 to B10 should use taxiway DELTA and LIMA (former INDIA).

Ground Traffic Management

In case of a landing on runway 29 no aircraft is allowed to be in the extended runway centreline of runway 29 while landing aircraft is passing above. In this case aircraft should hold at ROMEO, FOXTROTT, SIERRA and GOLF and wait until the incoming aircraft touched down.
You can also advise aircraft to follow behind another aircraft or give way to other taxiing aircraft.

Austrian 125, follow Airbus 320 to holding-point runway 29
Austrian 125, give way to taxiing Airbus 320 passing from left to right

When an aircraft is approaching its assigned holding-point (and clear of possible traffic-conflict) a hand-off to next higher position (i.e. TWR) shall be initiated as soon as possible.

Austrian 125, contact Tower on 119.40

Intersection take-off
Intersection takeoffs can be granted by GND in coordination with TWR and in accordance or on pilot’s request.

OE-ABC, wind xxx/xx runway 29 cleared for takeoff, after departure right turn as soon as practicable

Working Tower Positions

Tower is responsible for all movements on the runways as well as for all movements within the control zone (CTR), (10NM radius, GND to 2500ft MSL). Tower is also responsible for ground and delivery if they are not online. He also decides which runways are in use.

Determination of active Runways

Pilots normally prefer to takeoff and land the aircraft with the nose into the wind because it shortens the Rwy length required to safely operate the aircraft. The wind direction given in the METAR is the direction the wind is coming from, so it is easy to compare this wind to your given runways. Example:

You are the Tower controller at Salzburg Airport. The only runway at Salzburg is runway 16-34 so you have two directions available (roughly 160° and 340°.) The wind is coming from 180° at 5 knots. So the usual Runway in use would be rwy 16 for takeoff and landing.

However, at most airports a preferred runway configuration is defined (Find them here: Study Guide:Airport Details) which should be used if traffic situation and weather permits. Aircraft have certain limitations they can operate in, so normally the tailwind component should not exceed 5-10 knots (again depending on airport). Also the allowed crosswind is limited (This depends very much on the aircraft).
Be aware that it is the pilots responsibility to accept a certain wind component and that this decision is often based on performance issues, so one pilot might accept the next one refuses to take a certain runway.

So back to our example above:

At Salzburg, due to the terrain in the vicinity and city of Salzburg around the airport, runway 34 is preferred for departures and rwy 16 for landing. So the indicated configuration would be DEP 34, ARR 16.

Runway Separation

The runways are one of the most dangerous spots on an airport because aircraft are travelling at high speed with little room to maneuver and most of the time no ability to stop at a reasonable distance. Because of this the general rule is that only one aircaft may be cleared to use a runway at the same time. What this means practically and exceptions from this rule are explained in the following chapters.

Departing Traffic

So now we are at the point where the pilot reaches the Holding Point of his departure runway and reports ready for departure. What are the things you should check before issuing the takeoff clearance?

Have a look at the flightplan. Take note of the type of aircraft and the Departure Route.

Check the traffic approaching the runway.

To give him the takeoff clearance the following phrase should be used:

The pilot lines up on the runway, advances the throttle and takes off. When he is well established in climb check he is squawking Mode C and the right Code. Afterwards he is handed off to the next Controller, in this case a radar position:

The next aircraft reports ready for departure. Again check the points above, but this time we cannot give the takeoff clearance straight away because the preceeding aircraft is still occupying the runway. Now you get to know the first exception to the Runway Seperation rule above. To speed things up you can instruct the next aircraft to line up behind the first one while this one is still in the takeoff roll occupying the runway:

TWR: AZA639, behind departing Austrian Airbus A319, line-up rwy 29 behind and wait.
AZA639: behind departing Airbus lining up runway 29 and waiting behind, AZA639.
Note: The two times behind in this instruction is not a typing error but was implemented to emphasize that part of the clearance.

This type of clearance is called a conditional clearance.

The earliest possible point where you can issue the next takeoff clearance is, when the preceeding aircraft has overflown the opposite runway end or has clearly turned onto either side of it.
However in some cases this could be very close which leads us to the next chapter.

Departure Seperation - Based on Type of Aircraft and departure route

One of the main tasks of air traffic control is to keep aircraft at a safe distance to each other. So imagine the following situation:

Two aircraft are departing right after each other.

The first aircraft is a relatively slow Cessna 208 (~around 70 knots in climb), the second one a fast Boeing 767 (140-180 knots on the initial climb).

Both follow the same departure route.

Obviously it would not take long until the B767 catches up with the Cessna, a potentially very dangerous situation! You can see, that it is very important to check the flightplan of the aircraft you are about to clear for takeoff.
The minimum radar seperation in the area around an airport is 3 nm or 1000 feet. These are the limits radar stations have to obey. Tower Controllers should aim to achieve the following seperation for departing aircraft following departure routes which share a common part:

Fast followed by slow

3 nm

Matching Types

5 nm

Slow followed by fast

10 nm

In extreme examples like the one above it is often more advisable to coordinate with APP to find another solution. Often this involves clearing the aircraft to a non standard altitude or departure route:

The other main task of ATC is to expedite the flow of traffic. Situation:

You have numerous aircraft departing from the same runway, following different departure routes. Some of them involve immediate right turns other SIDs immediate left turns.

There are two holdingpoints available.

It would benificial to use the gaps that arise between the aircraft using similar Departure Routes, so in close coordination with ground you should try to distribute aircraft over the holding points in a way to be able to fill those gaps.

Departure Seperation - Based on Wake Turbulence Category

There are two ways aircraft influence the air around them when passing through it:

Jetwash produced by the engines

Turbulence created at the wings and especially at the wingtips

This turbulence can cause severe problems or even loss of control for following aircraft.
The wake turbulence categories are based on the Maximum Takeoff weight (MTOW) of the aircraft:

Light Aircraft (L)

< 7 000 kg

Medium Aircraft (M)

7 000 – 136 000 kg

Heavy Aircraft (H)

>136 000 kg

For departing aircraft, 2 minutes separation (3 minutes if the succeeding aircraft departs from an intersection) is applied when an aircraft in wake turbulence category LIGHT or MEDIUM departs behind an aircraft in wake turbulence category HEAVY, or when a LIGHT category aircraft departs behind a MEDIUM category aircraft.
You may issue a take-off clearance to an aircraft that has waived wake turbulence separation, except, if it's a light or medium aircraft departing as follows:

Behind a heavy a/c and takeoff is started from an interception or along the runway in the direction of take-off.

Behind a heavy a/c that is taking off or making a low or missed approach in the opposite direction on the same runway.

Behind a heavy a/c that is making a low or missed approach in the same direction of the runway.

To point out this hazard to a pilot the following phrase should be used:

VFR Traffic - Differences

VFR traffic can enter/leave the control zone (CTR) via sector SIERRA (to the south), sector ECHO (to the east) and along the Danube river on the route Klosterneuburg – Freudenau. Maximum altitude in these sectors is 1500ft or according to the VFR charts published online at www.vacc-sag.org.

VFR flights should be guided into downwind, base and final leg for landing.

Information Positions

Traffic Information

Weather Information

Special Requests

LOWW_I_APP (118.520) and LOVV_I_CTR (124.400) are the 2 FIS Positions within Austrian airspace. They are responsible for the VFR Flights. They allocate Squawks, provide Traffic Information and offer Weather Information (worldwide) and coordinate with other controllers requests from pilots.

You should assign top priority to inbound traffic not to outbound traffic to keep fluent traffic in rush-hour situations. In case of high traffic
the use of slots and departure intervals are recommended. A slot is a period of time in which a pilot should be airborne. One slot is followed by
another, continuously. Departure intervals are a certain period of time between two high traffic inbound waves. These departure intervals are used
to get rid of outbound traffic. Coordination with approach positions to ensure more spacing between inbounds is necessary.

OE-ABC, wind xxx/xx, runway 29 cleared for takeoff, after departure right turn as soon as practicable

Study Guide: Radar

Responsibilities

The responsibilities of a Radar Controller is to maintain the required seperation between aircrafts all the time by using different techniques of sequencing.

Airspace Structure

LOWW is located very close to the Austrian state boundaries with Hungary, Slovakia and the Czech Republik and space within the TMA (Terminal Maneuvering Area) is very limited.
Arrivals are being transferred to LOWW_APP by five independently working ACC sectors (LKAA/ACC Praha, LZBB/ACC Bratislava, LHCC/ACC Budapest, ACC Wien South, ACC Wien North). Therefore final decisions on the arrival sequence are normally made at a distance of approximately 40 NM from touchdown.

LOWW_APP itself operates up to four different sectors, depending on the amount of traffic. Two Upper Radar sectors specify the arrival sequence for the Lower Sectors. Upper Sectors are operated between FL240 and FL110.

The Lower Radar (FL100 and below) will then make final decisions on the arrival sequence by transferring arriving aircraft to the Director, who issues vectors onto the final approach track and sets up a safe flow of landing traffic. Unless otherwise instructed, initial contact on Director frequency (normally 119.800) shall be made by stating the callsign only in order to reduce frequency load.

When the appropriate spacing is assured until touchdown, Director will transfer the arriving aircraft to Tower.

Minimum Radar Separation

A Controller has to make sure that two Aircraft which are under his control never get closer than the minimum radar seperation. If two aircraft get closer than that, this incident is called a conflict.

The standard Minimum Vertical Seperation is 1000 ft up to FL290 and 2000 ft above that. However Austria is considered RVSM (Reduced Vertical Seperation Minima) airspace so the upper limit of the 1000 ft seperation minimum is raised to FL410. In real life this demands special equipment of the aircraft involved, however on VATSIM all aircraft are considered RVSM capable.

The Minimum Horizontal Seperation depends on the radar equipment involved. APP Sectors work with a minimum of 3 nm, CTR Sectors use 5 nm.

There are some cases where these minima may be under-run such as visual seperation or formation flights.

MRVA, MSA, MOCA

MRVA (Minimum Radar Vectoring Altitude): The MRVA is defined as the lowest available altitude above Mean Sea Level (MSL) in controlled airspace under consideration of the MSA (Minimum Safe/Sector Altitude) above ground and the airspace structure within a specified area.

MSA (Minimum Safe/Sector Altitude): Minimum Sector Altitude is the minimum altitude that may be used under emergency conditions which will provide a minimum clearance of 1000ft above obstacles and terrain contained within a sector of 25 NM radius centred on a radio navigational aid. MSA can be given as areas between radials from a VOR at the airport.

MOCA (Minimum Obstacle Clearance Altitude): This is the lowest altitude that an aircraft can fly in IMC (Instrument Meteorological Conditions) and still keep safe clearance from terrain and obstacles. MOCA is often lower then MEA (se below). It is only used in emergencies, especially to get below icing.

Structure of Flightplans and Routings

SIDs

SID (Standard Instrument Departure): It is a pre-defined route which aircrafts have to fly to get to their initial airway to follow their desired routing to their destination.

e.g.: Flightplan from LOWW (Wien) to Salzburg (LOWS): SITNI L856 SBG DCT - SITNI is our first waypoint of our routing and let us say for instance that in Vienna Runway 29 is in use. We take a look at our charts and we see that we can plan for a socalled SITNI4C departure route.

SIDs are specified by the local Air Traffic Control. A SID can contain the following navigation aids: R-NAV Waypoints, VORs, NDBs, etc.

STARs

STARs (Standart Terminal Arrival Routes): STARs are pre-defined routes to get an aircraft to the airport.

A STAR falls into three parts namely navigational point, version number and runway (depending on the airport), e.g. GAMLI4W arrival. The point at which the STAR ends is called Initial Approach Fix (IAF). In some cases the STARs continue and end at the Final Approach Fix (FAF), and that means that you as controller don't need to vector the aircraft unless there is other traffic in the way. The only thing you have to do is to instruct the pilot how to descend the aircraft.

There are exceptions of course, where the STARs don't end at the final, but at a navigational point some distance away from the runway. You as a controller must give vectors the last part to the runway. If you for some reason don’t give vectors, the pilot must enter holding at the STAR's ending point (clearance limit).

Types of Instrument Approaches

An instrument approach or instrument approach procedure (IAP) is a type of air navigation that allows pilots to land an aircraft in reduced visibility (Instrument Meteorological Conditions [IMC]) or to reach visual conditions permitting a visual landing.

Seperation and Sequencing Techniques

Planning

LOWW_APP is aiming at a maximum of 15 minutes flight extension for sequencing of arrivals to LOWW within the TMA (Terminal Maneuvering Area). Arriving aircraft will normally get radar vectors to one common downwind.

Vectoring

There are 2 types of vectoring:

Lateral Vectoring

Vertical Vectoring

1.) Lateral Vectoring

- ABC123, turn left heading 165°
- DEF243, turn right heading 300°

When issuing a heading to an aircraft, make sure that you are using a direction ending on 0 (zero) or on 5 (five).

If you provide Radar Vectors to an aircraft then always tell the pilot the reason why you are doing this:

As you can see there are 2 types of heights namely Altitude and Flightlevel (FL).

Flightlevel is used for aircraft flying above the Transition Altitude, Transition Level or climbing through and above the Transition Layer (Altimeter in the aircraft is set to Standart Pressure [1013 QNE]).

Altitude is used for aircraft flying below the Transition Altitude or for Aircraft descending through and below the Transition Layer (Altimeter in the aircraft is set to local QNH).

Holding

Useage

The primary use of a holding is delaying aircraft that have arrived over their destination but cannot land yet because of traffic congestion, poor weather, or unavailability of the runway. Several aircraft may fly the same holding pattern at the same time, separated vertically by 1,000 feet or more.

Flying a Hold

Most aircraft have a specific holding speed published by the manufacturer.Maximum holding speeds are established in order to keep aircraft within the protected holding area during their one-minute inbound and outbound legs.

As a rule of thumb the Speed to be flown depends on the altitude or flight level the aircraft is at within the hold as follows:

- A clearance to the holding fix.
- The direction to hold from the holding fix.
- A specified radial, course, or inbound track.
- If DME is used, the DME distances at which the fix end and outbound end turns are to be commenced.
- The altitude or FL to be maintained.
- The time to expect further clearance or an approach clearance.
- The time to leave the fix in the event of a communications failure.

Standart Holding Pattern

* Standard Hold: A hold where all turns are made to the right
* Non Standard Hold: A hold where all turns are made to the left
* Holding Course: The course flown on the inbound leg to the holding fix.
* Inbound Leg: The standard 1 or 1.5 minute leg to the holding fix as Published
* Holding Fix: This can be a VOR, a VORDME, an Intersection or an NDB
* Outbound Turn: A standard rate, 180 degrees turn which is begun at the holding Fix.
* Abeam: The position opposite the holding fix, where the outbound begins.
* Outbound Leg: This leg is defined by the inbound leg, pilots should adjust the outbound leg so that the inbound turn, the other standard 180° turn is completed just as the holding course is intercepted.
* Holding Side: The side of the course where the hold is accomplished.
* Non Holding Side: The side of the course where you do not want the pilot to be holding

Non Standart Holding Pattern

A non-standard holding pattern is one in which

- The fix end and outbound end turns are to the left; and/or
- The planned time along the inbound track is other than the standard one-minute or one-and-a-half minute leg appropriate for the altitude flown.

Entry Holding Procedure

Direct Entry (aircraft flies directly to the holding fix, and immediately begins the first turn outbound)

Parallel Entry (aircraft flies to the holding fix, parallels the inbound course for one minute outbound, and then turns back, flies directly to the fix, and proceeds in the hold from there

Teardrop Entry or Offset Entry (aircraft flies to the holding fix, turns into the protected area, flies for one minute, and then turns back inbound, proceeds to the fix and continues from there).

Coordination with adjacent Sectors

The coordination respectively the communication between controllers (and of course pilots) is on of the most important things in aviation.

A clear instruction to the person I want to speak to falls into 4 parts:

- Who am I calling
- What do I want
- How are we going to archieve this (short and clear instructions!)
- Did the person I called unterstand my instruction properly

VFR Traffic

Flight Information Positions

Flight Information Service (FIS) is an air traffic facility that provides a myriad of services to the pilot, such as pilot briefings, relaying of clearances and broadcasting of weather information.
At selected locations, FIS also provides en-route Flight Advisory Services.

Abnormal Situations - Emergencies, Radio Failures

Emergencies

Emergencies are very uncomfortable situations for every controller. Emergencies shall be handeled expeditiously to get them safe down to the ground.

Note: The pilot tells the ATC what his intentions are and what he will do next and not the other way round. ATC keeps all the traffic in the vicinity of the emergency aircraft away to assure that no other aircraft gets injured.

All Weather Operations (AWO)
With Low Visibility Procedures in operation, standard approach runway will be runway 16.
Arrivals will be vectored out of the holdings into the left hand circuit for runway 16. Approximate track distance from the holdings to touchdown shall be calculated with 40 to 70 nautical miles.

Controlling CTR Positions

Area Control Center (ACC) provides ATC to aircraft on the en-route phase of flight.
This includes giving information that the pilot needs such as weather and traffic information. The ACC controller has to assure that the seperation is always appropriate regarding to the traffic in the vicinity ( 5 nautical miles lateral, 1000 feet vertical at least ).

ACC is also responsible for all airports where Tower and Approach are not manned. If you are working on the ACC position always remember that this position is a demanding position and requires great knowledge and experience.

Study Guide: Airport Details

LOWW (Wien Schwechat)

Pisten

11/29: Beton, 3500x45 Meter, ILS

16/34: Beton, 3600x45 Meter, ILS

Visual Approches

Approaches using "Own Separation". Visual Approaches will be issued whenever the traffic situation permits. Due to several noise sensitive areas in the vicinity of Vienna Airport, LOWW_APP has to impose certain restrictions on visual approaches:

NO visual or short approaches will be issued in the right-hand circuit for runway 16 and in the left-hand circuit for runway 11 (City of Vienna).

Aircraft instructed to "maintain own separation" during final approach are expected to maintain a safe and efficient separation (normally less than 2,5 NM) to the preceding landing aircraft.

Possible Runway Configurations

The runway utilization concept for LOWW is based on the fact that the airport layout with it's crossing runways normally does not allow simultaneous approaches to both runways. So, whenever possible, runways 11/29 and 16/34 will be used independently to allow departures on one runway (normally 16 or 29) while using the other runway for landing aircraft.

Simultaneous approaches to runways 11 and 16 are conducted only at tower's discretion during certain weather conditions (visual reduction of separation). Aircrews are advised to show landing lights as soon as possible.
In case of technical uncertainties during final approach - that might be possible lead to a missed approach - aircrews are asked to inform ATC immediately.